U.S. Pat. No. 5,284,211 and International Patent Application No. WO/1996/009440 disclose debris collection devices suitable, for example, for collecting small debris from a ground surface. These are each in the form of a mat-like structure having openings therethrough. The mat-like structure is laid on the ground surface and moved over the surface so the debris passes from the ground surface upwardly through the openings to rest on the upper surface of the structure. The device may then be moved to a suitable location at which the collected debris on the upper surface of the structure is removed, such as by up-ending the device. For example, the device of U.S. Pat. No. 5,284,211 has been found useful for clearing leaves from, and generally grooming, en tout cas tennis courts, and the arrangement of WO/1996/009440 useful for a variety of applications, including clearing debris such as bolts, screws, nuts washers and other foreign object debris, so called “FOD”, from aircraft runways.
Arrangements such as shown in U.S. Pat. No. 5,284,211 and international application WO/1996/009440 have been found to be very satisfactory in use, offering a relatively inexpensive alternative to, for example, mechanical sweeping devices using rotary brushes. However, it has been noticed that, sometimes, there is a tendency for collected material on the mat structure to fall back through the openings in it, and be lost again. This tendency particularly occurs under abrupt deceleration of the device when it is being moved over the ground surface. Loss of collection efficiency due to this can be limited by ensuring that this deceleration is always relatively gentle, but it would be advantageous to be freer of this operational constraint.
International Patent Application No. PCT/AU2008/001252 describes a device for collecting debris from a ground surface, comprising a flexible generally planar member with an opening therethrough such that when the device is laid on and forwardly moved over a ground surface debris on the ground surface passes upwardly through the opening onto a collection surface of the device, the device having a transversely extending barrier positioned whereby, in use, debris passing upwardly through the opening passes upwardly over the barrier and then downwardly to the collection surface, the barrier at least partially obstructing movement of collected debris on the collection surface back into the opening under deceleration of the device as it is forwardly moved over the ground surface.
This has been found to greatly facilitate retention of debris during deceleration as mentioned, but even greater efficiency in that regard would be desirable.